1. Field of the Invention
The present invention generally relates to a thin film apparatus, a manufacturing method of the thin film apparatus, an active matrix substrate, a manufacturing method of the active matrix substrate, and an electro-optical apparatus having the active matrix substrate, and more particularly technologies whereby the thin film device is formed on the substrate and then peeled from the substrate.
2. Description of the Related Art
A semiconductor process is utilized for manufacturing a thin film transistor (hereinafter “TFT”), as a switching element, on a substrate for an active matrix type liquid crystal display apparatus using a liquid crystal as electro-optical material. Since the above mentioned process includes a step having a high temperature process, it is necessary to use a substrate made of material having good heat resistance, namely material having both a high softening point and a high melting point. Therefore, presently, quartz glass is used as a substrate that can resist a temperature of approximately 1000 degrees centigrade and a heat resistant glass is used as a substrate that can resist temperature of approximately 500 degrees centigrade.
Thus, a substrate where the thin film device such as the TFT is provided can resist a temperature condition or the like for manufacturing the thin film device. However, the above mentioned quartz glass or heat resistant glass is not always advantageous after the substrate where thin film device such as the TFT is provided is completed. For example, in a case where the quartz glass or the heat resistant glass is used for resisting the manufacturing process having the heat temperature process, the product price of the display apparatus or the like is high, as these substrates are extremely expensive.
In addition, it is required for the display apparatus used for a portable electronic machine, such as a palm top computer or a portable phone, to have a price as low as possible, a light weight, some resistance to deformation, and a resistance to splitting even if the display apparatus is dropped. However, the quartz glass or the heat resistant glass is heavy, poor at resisting deformations and easy to become split if the display apparatus is dropped. Accordingly, the substrate used for the conventional thin film apparatus has problems in that the substrate is not suited for limitations in terms of manufacturing conditions and characteristics required for the product.
Meanwhile, Japanese Laid-Open Patent Application No. 10-125929 discloses a technology whereby after a polycrystalline silicon TFT is formed on a first substrate under conditions equivalent to conventional processes, the thin film device is peeled from the first substrate and transferred to a second substrate. A separation layer is formed between the first substrate and the thin film device and energy light, for example, is projected onto the separation layer. As a result of this, the thin film device is peeled from the first substrate and transferred to a side of the second substrate.
Recently, an organic TFT and an organic electroluminescent (hereinafter “EL”) element have been studied as organic thin film electronic devices, and a manufacturing an organic EL display driven by an organic TFT active matrix driving has been attempted as an application of the organic TFT and the organic EL element. The organic electronic device does not need expensive manufacturing equipment to be manufactured, unlike the polycrystalline silicon TFT. The organic electronic device can be manufactured cheaply and is suitable as a display apparatus used for the above mentioned palm top computer and the portable electronic machine such as the portable phone.
In a case where the above mentioned organic TFT is formed on a plastic sheet (substrate), it is very difficult to directly form the active element thereon, because the substrate is poor at measurement stability.
Japanese Laid-Open Patent Application No. 8-62591 discloses a technology whereby an active matrix layer, pre-formed on a substrate having good heat resistance such as glass, is transferred onto the plastic sheet substrate. In the technology disclosed in the Japanese Laid-Open Patent Application No. 8-62591, complex steps, such as application of metal plating to a release layer and providing a transparent electric insulation layer to the active matrix layer, are required. In addition, the technology disclosed in the Japanese Laid-Open Patent Application No. 8-62591 has a problem of stress being generated due to use of a solvent type pressure-sensitive adhesive composition as an adhesive composition. Furthermore, Japanese Laid-Open Patent Application No. 2001-356370 discloses complex steps whereby a slit is additionally formed and an inorganic buffer layer is arranged in order to protect the active matrix layer from an external force at the time of transferring.
According to the above mentioned technologies, a release separation layer is formed and transferred to second and third substrates, so that an active matrix substrate is formed on a flexible sheet having a large area.
An important technology with regard to a transferring method is a peeling step. The above mentioned technologies can be divided into: methods for a reduction of an adhering force based on a phase change phenomena by laser irradiation applied to amorphous silicon, and a reduction of an adhering force based on radiation irradiation (Japanese Laid-Open Patent Application No. 8-152512); a method for physical and chemical removal of a substrate (Japanese Laid-Open Patent Applications No. 10-189924 and No. 11-31828); and a method for protecting an element from a stress-generating mechanical peeling.
However, there is a problem in that the peeling phenomenon at the separation layer is not properly generated in the conventional peeling method and transferring method. Furthermore, there is a conventional limitation of the size of the substrate, so that it is impossible to apply an element having a large area, which is a specific future requirement of organic electronic devices.